The invention relates to an apparatus for regulating the temperature in a room or a compartment. More particularly, the invention relates to controlling the temperature of the passenger compartment of a motor vehicle which is equipped with an air conditioning system that includes a heat exchanger for cooling and a second heat exchanger for the purpose of providing heated air. The supply line for the heating medium includes a final control element which is adjusted on the basis of information from a compartment temperature sensor which is compared with the reference or set-point temperature.
In a known system of this type, the air is accelerated by a blower and passes sequentially through a cooler and a heating radiator. The automatic control is confined to the adjustment of the heating power of the heating radiator.
In another apparatus of this type, the amount of air which passes through the heater or the cooler is adjusted by air flow directing elements on the basis of compartment temperature and external temperature while the quantity of the heating medium through the heater is also controlled by a valve.
An inherent disadvantage of the known apparatus is that the cooler assembly which delivers refrigerant into the cooling heat exchanger is in operation at all times and the desired air temperature must be adjusted with an additional and quite expensive control system for the heating plant that must have a large control domain. Furthermore, the straightforward temperature monitoring results in relatively wide control swings. In addition, the constantly operating refrigerating unit requires substantial energy which must be supplied by the engine. A second disadvantage in the known apparatus is that the various flaps and valves are subject to a high probability of failure and the rapidly and widely varying air flow rates through the heat exchangers do not permit a quick and exact temperature control because of the inherent hysteresis of changes of temperature.